Answer in brief
CVE-2021-46936 records a High severity (CVSS 7.8) vulnerability in net: fix use-after-free in tw_timer_handler. The current sources do not mark it as known exploited. The current feed maps Linux/Linux (generic), Linux/Linux (generic). Check affected ranges and fixed versions before updating.
Analysis pending evidence review
HOL Guard separates source facts from reviewed analysis. See the methodology.
Answer in brief
CVE-2021-46936 records a High severity (CVSS 7.8) vulnerability in net: fix use-after-free in tw_timer_handler. The current sources do not mark it as known exploited. The current feed maps Linux/Linux (generic), Linux/Linux (generic). Check affected ranges and fixed versions before updating.
Analysis pending evidence review
HOL Guard separates source facts from reviewed analysis. See the methodology.
CVSS is 7.8. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.
Analysis status
Analysis pending evidence review
Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.
The current feed maps Linux/Linux (generic), Linux/Linux (generic). Check affected ranges and fixed versions before updating.
| Product | Affected versions | Fixed versions |
|---|---|---|
| cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* | Not reported | Not reported |
| Package | Affected range | Fixed version |
|---|---|---|
| Linux/Linuxgeneric | >=61a7e26028b94805fd686a6dc9dbd9941f8f19b0 <15579e1301f856ad9385d720c9267c11032a5022 || >=61a7e26028b94805fd686a6dc9dbd9941f8f19b0 <e73164e89d1be561228a4534e1091369ee4ba41a || >=61a7e26028b94805fd686a6dc9dbd9941f8f19b0 <5c2fe20ad37ff56070ae0acb34152333976929b4 || >=61a7e26028b94805fd686a6dc9dbd9941f8f19b0 <a8e1944b44f94f5c5f530e434c5eaee787254566 || >=61a7e26028b94805fd686a6dc9dbd9941f8f19b0 <fe5838c22b986c1190f1dce9aa09bf6a491c1a69 || >=61a7e26028b94805fd686a6dc9dbd9941f8f19b0 <2386e81a1d277f540e1285565c9d41d531bb69d4 || >=61a7e26028b94805fd686a6dc9dbd9941f8f19b0 <08eacbd141e2495d2fcdde84358a06c4f95cbb13 || >=61a7e26028b94805fd686a6dc9dbd9941f8f19b0 <e22e45fc9e41bf9fcc1e92cfb78eb92786728ef0 | 15579e1301f856ad9385d720c9267c11032a5022, e73164e89d1be561228a4534e1091369ee4ba41a, 5c2fe20ad37ff56070ae0acb34152333976929b4, a8e1944b44f94f5c5f530e434c5eaee787254566, fe5838c22b986c1190f1dce9aa09bf6a491c1a69, 2386e81a1d277f540e1285565c9d41d531bb69d4, 08eacbd141e2495d2fcdde84358a06c4f95cbb13, e22e45fc9e41bf9fcc1e92cfb78eb92786728ef0 |
| Linux/Linuxgeneric | 2.6.27 | Not reported |
Published upstream
Feb 27, 2024
Evidence: source:cvelist:source_dates:source-dates:recordSource modified
Aug 4, 2026
Evidence: source:cvelist:source_dates:source-dates:recordFirst seen by HOL
Aug 4, 2026
In the Linux kernel, the following vulnerability has been resolved: net: fix use-after-free in tw_timer_handler A real world panic issue was found as follow in Linux 5.4. BUG: unable to handle page fault for address: ffffde49a863de28 PGD 7e6fe62067 P4D 7e6fe62067 PUD 7e6fe63067 PMD f51e064067 PTE 0 RIP: 0010:tw_timer_handler+0x20/0x40 Call Trace: <IRQ> call_timer_fn+0x2b/0x120 run_timer_softirq+0x1ef/0x450 __do_softirq+0x10d/0x2b8 irq_exit+0xc7/0xd0 smp_apic_timer_interrupt+0x68/0x120 apic_timer_interrupt+0xf/0x20 This issue was also reported since 2017 in the thread [1], unfortunately, the issue was still can be reproduced after fixing DCCP. The ipv4_mib_exit_net is called before tcp_sk_exit_batch when a net namespace is destroyed since tcp_sk_ops is registered befrore ipv4_mib_ops, which means tcp_sk_ops is in the front of ipv4_mib_ops in the list of pernet_list. There will be a use-after-free on net->mib.net_statistics in tw_timer_handler after ipv4_mib_exit_net if there are some inflight time-wait timers. This bug is not introduced by commit f2bf415cfed7 ("mib: add net to NET_ADD_STATS_BH") since the net_statistics is a global variable instead of dynamic allocation and freeing. Actually, commit 61a7e26028b9 ("mib: put net statistics on struct net") introduces the bug since it put net statistics on struct net and free it when net namespace is destroyed. Moving init_ipv4_mibs() to the front of tcp_init() to fix this bug and replace pr_crit() with panic() since continuing is meaningless when init_ipv4_mibs() fails. [1] https://groups.google.com/g/syzkaller/c/p1tn-_Kc6l4/m/smuL_FMAAgAJ?pli=1
Quoted source text, attributed separately from HOL analysis.
CVSS is 7.8. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.
Analysis status
Analysis pending evidence review
Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.
The current feed maps Linux/Linux (generic), Linux/Linux (generic). Check affected ranges and fixed versions before updating.
| Product | Affected versions | Fixed versions |
|---|---|---|
| cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* | Not reported | Not reported |
| Package | Affected range | Fixed version |
|---|---|---|
| Linux/Linuxgeneric | >=61a7e26028b94805fd686a6dc9dbd9941f8f19b0 <15579e1301f856ad9385d720c9267c11032a5022 || >=61a7e26028b94805fd686a6dc9dbd9941f8f19b0 <e73164e89d1be561228a4534e1091369ee4ba41a || >=61a7e26028b94805fd686a6dc9dbd9941f8f19b0 <5c2fe20ad37ff56070ae0acb34152333976929b4 || >=61a7e26028b94805fd686a6dc9dbd9941f8f19b0 <a8e1944b44f94f5c5f530e434c5eaee787254566 || >=61a7e26028b94805fd686a6dc9dbd9941f8f19b0 <fe5838c22b986c1190f1dce9aa09bf6a491c1a69 || >=61a7e26028b94805fd686a6dc9dbd9941f8f19b0 <2386e81a1d277f540e1285565c9d41d531bb69d4 || >=61a7e26028b94805fd686a6dc9dbd9941f8f19b0 <08eacbd141e2495d2fcdde84358a06c4f95cbb13 || >=61a7e26028b94805fd686a6dc9dbd9941f8f19b0 <e22e45fc9e41bf9fcc1e92cfb78eb92786728ef0 | 15579e1301f856ad9385d720c9267c11032a5022, e73164e89d1be561228a4534e1091369ee4ba41a, 5c2fe20ad37ff56070ae0acb34152333976929b4, a8e1944b44f94f5c5f530e434c5eaee787254566, fe5838c22b986c1190f1dce9aa09bf6a491c1a69, 2386e81a1d277f540e1285565c9d41d531bb69d4, 08eacbd141e2495d2fcdde84358a06c4f95cbb13, e22e45fc9e41bf9fcc1e92cfb78eb92786728ef0 |
| Linux/Linuxgeneric | 2.6.27 | Not reported |
Published upstream
Feb 27, 2024
Evidence: source:cvelist:source_dates:source-dates:recordSource modified
Aug 4, 2026
Evidence: source:cvelist:source_dates:source-dates:recordFirst seen by HOL
Aug 4, 2026
In the Linux kernel, the following vulnerability has been resolved: net: fix use-after-free in tw_timer_handler A real world panic issue was found as follow in Linux 5.4. BUG: unable to handle page fault for address: ffffde49a863de28 PGD 7e6fe62067 P4D 7e6fe62067 PUD 7e6fe63067 PMD f51e064067 PTE 0 RIP: 0010:tw_timer_handler+0x20/0x40 Call Trace: <IRQ> call_timer_fn+0x2b/0x120 run_timer_softirq+0x1ef/0x450 __do_softirq+0x10d/0x2b8 irq_exit+0xc7/0xd0 smp_apic_timer_interrupt+0x68/0x120 apic_timer_interrupt+0xf/0x20 This issue was also reported since 2017 in the thread [1], unfortunately, the issue was still can be reproduced after fixing DCCP. The ipv4_mib_exit_net is called before tcp_sk_exit_batch when a net namespace is destroyed since tcp_sk_ops is registered befrore ipv4_mib_ops, which means tcp_sk_ops is in the front of ipv4_mib_ops in the list of pernet_list. There will be a use-after-free on net->mib.net_statistics in tw_timer_handler after ipv4_mib_exit_net if there are some inflight time-wait timers. This bug is not introduced by commit f2bf415cfed7 ("mib: add net to NET_ADD_STATS_BH") since the net_statistics is a global variable instead of dynamic allocation and freeing. Actually, commit 61a7e26028b9 ("mib: put net statistics on struct net") introduces the bug since it put net statistics on struct net and free it when net namespace is destroyed. Moving init_ipv4_mibs() to the front of tcp_init() to fix this bug and replace pr_crit() with panic() since continuing is meaningless when init_ipv4_mibs() fails. [1] https://groups.google.com/g/syzkaller/c/p1tn-_Kc6l4/m/smuL_FMAAgAJ?pli=1
Quoted source text, attributed separately from HOL analysis.